This invention generally pertains to a technique for incorporating antimicrobial agents into fibers following the melt spinning step in fiber manufacturing processes. The process of the invention results in a fiber having an essentially homogeneous distribution of the agent throughout the fiber cross-section. This invention is contrasted with prior art activities which have either focused upon surface treatment with antimicrobial agents or upon melt incorporation to achieve essentially uniform distribution throughout the fiber cross-section. Surface treatment techniques are illustrated by U.S. Pat. No. 4,408,996.
Antimicrobial agents, such as 10,10'-oxybisphenoxarsine, (OBPA), are known to serve to provide protection against bacterial attack of thermoplastic fiber materials, such as Nylon 6. The incorporation of OBPA also serves to reduce the occurrence of mildew and other undesirable growth on the fiber when in final product form such as carpeting. OBPA has been incorporated into molten nylon so as to be included in as-spun fiber. This results in an essentially homogeneous distribution of the agent through the fiber cross-section. U.S. Pat. No. 3,345,341 is illustrative of such prior techniques.
However, melt incorporation is unsatisfactory for many antimicrobial agents such as bis(tri-n-butyl tin)oxide (TBTO), because the temperatures of the molten fiber material are sufficiently high to destroy the effectiveness of the agent. Hence, a lower temperature incorporation alternative technique provides considerable attractiveness to the fiber industry.
In addition, it is not uncommon in the industry to encounter losses of antimicrobial agent during the dyeing operations which range up to about 70%. These losses are believed to be caused by leaching of the antimicrobial agent resulting in an equilibrium proportioning of the agent between the solid phase (fiber) and the liquid phase (dye bath medium).
In the past, this problem has been avoided by solution dyeing in which the dye is incorporated into the melt along with the antimicrobial agent at the melt-spinning state. For example, nylon carpet containing melt incorporated OBPA is currently manufactured in this manner. However, solution dyed carpeting is only available in a rather limited number of shades and, of course, can only be dyed by the fiber manufacturer. It would be desirable for the carpet manufacturers to be able to process undyed bulk fiber into carpeting by incorporating an antimicrobial agent homogeneously throughout the carpet fiber during or subsequent to the dyeing process. This procedure would provide greater latitude as to color selection and would provide greater flexibility for the overall manufacturing process. It is believed that the process of this invention overcomes the above mentioned problems in a highly advantageous and efficient manner by adding or exhausting the antimicrobial agent into the fiber only in the amount ultimately required during the dyeing step.